1. Technical Field
The present invention relates to a lens barrel including an eccentricity adjusting mechanism, in particular, to a lens barrel including an eccentricity adjusting mechanism for improving optical performance (a resolution level or others) by rotating a predetermined lens constructing an optical system of the lens barrel around an optical axis of the lens barrel.
2. Related Art
Generally, in case of a lens barrel for use in a TV camera or others for broadcasting or business, the adjustment of eccentricity of a lens to increase optical performance such as MTF (resolution) is carried out while the image formation state (image quality) of the lens is observed by a collimator attached onto a leading end of the lens after the lens is fitted into the lens barrel (inside a fixed barrel). The adjustment of eccentricity of a lens is realized by carrying out position adjustment in a direction orthogonal to an optical axis, rotation adjustment around an optical axis, slant angle adjustment, or others.
Conventionally, in order to realize the eccentricity adjustment in the state that all lenses are fitted into the barrel and an optical system is complated, an eccentricity adjusting mechanism enabling the eccentricity adjustment by moving some lenses largely influencing the optical performance by using a tool or the like from the outside of the lens barrel has been suggested.
For example, according to the eccentricity adjusting mechanism of JP-A-2000-66076, some of a lens group having a plurality of lenses integrally held in an outer lens frame are held as lenses to be subjected to eccentricity adjustment in an inner lens frame disposed in the inside of the outer lens frame. The outer lens frame is axially supported by an eccentric pin engaged with the inner lens frame. The eccentric pin is rotated through a hole penetrating from the outside of the barrel to the eccentric pin, thereby adjusting a slant angle of the lenses in the inner lens frame.
According to the eccentricity adjusting mechanism of JP-A-2000-75182, a lens group having a plurality of lenses is held in the outer lens frame, as in JP-A-2000-66076. Some of the lens groups are held as lenses to be subjected to eccentricity adjustment in the inner lens frame. A gear is provided on the circumferential surface of the inner lens frame. The inner lens frame is rotated by a rotating means engaged with the gear through an aperture penetrating from the outside of the barrel to the gear, thereby adjusting rotation of the lenses of the inner lens frame around the optical axis.
According to the eccentricity adjusting mechanism of JP-A-H11-174301, an exposed part is provided in a lens frame holding lenses to be subjected to eccentricity adjustment in the direction orthogonal to the optical axis, and exposed from the outside of the barrel. The exposed part is displaced by an adjustment jig, thereby adjusting the position of the lenses in the direction orthogonal to the optical axis.
However, if eccentricity adjustment is carried out by rotating the lens frame around the optical axis as in Patent Document 2, the rotation direction may be problematic. For example, in case of rotating the outer lens frame (referred to as simply the “lens frame”) itself, rather than the inner lens frame disposed in the outer lens frame, sandwiching a predetermined site of the lens frame between a predetermined site of the fixed barrel and a pressing ring screw-connected to the fixed barrel has been known as a structure for rotatably supporting the lens frame to the fixed barrel. In the structure for supporting the lens frame, when the lens frame is rotated around the optical axis, if the lens frame is rotated in a direction to loosen the pressing ring screw-connected to the fixed barrel, the rotating force of the lens frame is transferred to the pressing ring so that the pressing ring may be loosened. If the pressing ring is loosened, the lens frame clatters in the optical axis direction so that the optical performance is deteriorated. If this problem occurs when eccentricity adjustment is carried out in the state that all lenses are fitted in the fixed barrel, one should undergo hard works for disassembling the lens barrel and engaging the pressing ring once again.
With respect to a method for regulating the lens frame to be rotated in one direction upon eccentricity adjustment, providing a ratchet mechanism between the pressing ring and the lens frame may be considered. However, providing the ratchet mechanism increases manufacturing costs. Further, the lens frame may easily clatter in the optical axis direction due to vibration or other causes, thereby causing deterioration of the optical performance. Accordingly, it is desirable to regulate (restrain) the rotation of the lens frame in the direction to loosen the pressing ring, without providing a special mechanism.
The present invention has been made in consideration of the circumstances, and its object is to provide a lens barrel having an eccentricity adjusting mechanism, in which a lens frame holding lenses to be rotated for eccentricity adjustment is rotatably supported to a fixed barrel by a pressing ring screw-connected to the fixed barrel, such that upon the eccentricity adjustment, a worker is restrained from rotating the lens frame in the direction to loosen the pressing ring screw-connected to the fixed barrel, thereby preventing the pressing ring from being loosened due to the eccentricity adjustment.